1. Field
Various features pertain to wideband and ultra-wideband communication systems. At least one aspect pertains to eliminating or reducing the effects of frequency domain spreading of narrowband interference (NBI) in wideband and ultra-wideband communication systems.
2. Background
One modern transmission technique is known as Orthogonal Frequency-Division Multiplexing (OFDM) which uses orthogonality between a plurality of sub-carriers to make data sequences independent from each other. OFDM provides high spectral efficiency, can adapt to severe channel conditions without complex equalization, and is robust against narrow-band co-channel interference. Consequently, signal orthogonality can be maintained in the presence of multipath channels and linear filters. Because the plurality of orthogonal sub-carriers can use a lower symbol rate modulation, this eliminates intersymbol interference (ISI) to which a single, high symbol rate channel is susceptible.
OFDM may be implemented in wideband communication systems, such as ultra-wideband (UWB). UWB communication systems transmit information over a large bandwidth in a way that does not interfere with traditional narrowband communications. However, UWB transmissions are affected by narrowband interference (NBI). Such interference may be concentrated on one or two narrowbands or tones (for example). Filtering these narrowbands does not entirely cancel NBI. Windowing, such as a square or rectangular window function, is applied by a receiver in the time domain to obtain each OFDM symbol. However, while windowing is applied in the time domain of each OFDM symbol, the NBI spreads in frequency domain like a sinc function. That is, the NBI generates side lobes that decrease relatively slowly. Consequently, a larger portion of the bandwidth spectrum is affected by the side lobes than just the one or two narrowbands or tones.
Therefore, a method is needed that reduces or eliminates NBI within wideband or ultra-wideband communication systems.